Looping with forEach

Learn to traverse an array with forEach and the callback idea.

Traversing an array with forEach

To traverse all elements of an array you use the forEach method. forEach runs a callback function for each element.

Example: fruits.forEach(fruit => console.log(fruit)); prints each element of the array in order.

forEach does not return a new array; its return value is undefined. So it is not suitable for collecting results, only for processing elements one by one.

fruit => console.log(fruit) is a short way to write a function (an arrow function): the left of the arrow is the parameter, the right is the expression to run. It does the same as function (fruit) { console.log(fruit); }; you will cover it in detail at the intermediate level.

The three parameters of forEach

The callback function can take three parameters: (element, index, array). Only the first is required; you use the others as needed.

Example: fruits.forEach((fruit, i) => console.log(i + ". " + fruit)); prints each element together with its index.

The second parameter is the index, the third is the array itself. Names do not matter; the order does.

Exercise Print the fruits array with forEach

Create an array named fruits with at least three fruit strings. Use forEach to print each element with console.log.

Show example solution

Write the array with square brackets, then pass a callback to forEach.
Example solution:
const fruits = ["apple", "pear", "banana"];
fruits.forEach(fruit => console.log(fruit));

Test yourself

How many times does console.log run in this code?
```
const nums = [10, 20, 30];
nums.forEach(n => console.log(n));
```
- 1
- 3
- 0
- 2
Show answer

3 — Correct. forEach calls the callback for each element; 3 elements means 3 calls.

Print each element with forEach

const fruits = ["apple", "pear", "banana"];
fruits.forEach(fruit => console.log(____));

Show answer

const fruits = ["apple", "pear", "banana"];
fruits.forEach(fruit => console.log(fruit));

Match the forEach callback parameters

1st parameter

element value
2nd parameter

element index
3rd parameter

the array itself

Next lesson: The for...of loop

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